It is proposed to determine the role played by vitamin K in the vitamin K dependent carboxylation of the gamma carbon of specfic glutamic acid residues of precursos proteins in the liver. In order to do this, it will be necessary to determine all the components of the in vitro vitamin K dependent system and role played by each in the overall carboxylation reaction. All protein (substrate aad enzyme) requiremtns are located in the microsomal fraction of rat liver homogenates. These fractions are being fractionated to isolate and determine the number required and their function. The added components (non-protein) required for the system to function have been determined. Their individual functions are being investigated. BIBLIOGRAPHIC REFERENCES: Chung, G.C.H., Delaney, R., Mack, D. and Johnson, B.C. Partial Purification and Characterization of the Enzyme which Converts Precursor Liver Protein to Factor X. Biophys. Acta 386(2), 556-566 (1975). Mack, D.O., Girardot, J.M., Chung, G., Delaney, R. and Johnson, B.C. The Vitamin K-Dependent Enzyme and Enzyme Substrate of Rat Liver. Fed. Proc. 34(3), Abstract No. 224 (1975).